Vacuum deposited silver halide photographic element



United States Patent 3,384,490 VACUUM DEPOSITED SILVER HALIDE PHOTOGRAPHZC ELEMENT William W. Rees, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New .lersey No Drawing. Filed Dec. 28, 1964, Ser. No. 421,725 7 Claims. (Cl. 96-410) ABSTRACT OF THE DISCLOSURE Photographic elements, incorporating a binderless layer of vacuum-deposited silver halide as the light-sensitive component, can be chemically sensitized with gold and other metal salts without an increase in fog by including the combination of a thiosulfate salt and a thiocyanate salt as an antifoggant.

This invention relates to the chemical sensitization of photographic elements having as a light sensitive layer an essentially binder-free deposit of silver halide.

It is known to provide photographic elements having a light sensitive layer of binder-free silver halide. Such elements may be prepared, for example, by vacuum deposition of silver halide on a suitable support. These elements have advantages in rapid processing, good acutance and ease and economy of preparation. However, one disadvantage of such elements is their relatively low sensitivity as compared to conventional silver halide emulsions. It has been found that good increases in sensitivity of the present elements may be realized by various chemical sensitizers, but that many of these sensitizers cause an undesirable increase in fog. it would be highly desirable if photographic elements having as a light sensitive layer a binder-free deposit of silver halide could be sensitized with chemical sensitizers, without inducing fog.

One object of this invention is to provide novel photographic elements having a chemically sensitized lightsensitive layer of silver halide that is substantially free from binder, which sensitized elements exhibit low fog. A further object of this invention is the sensitization of photographic elements having a light sensitive, binderfree layer of silver halide, with the combination of a chemical sensitizer and a substance which coacts with the chemical sensitizer to substantially reduce fog Another object of this invention is to provide a novel method of sensilizing photographic elements having a light sensitive, binder-free layer of silver halide, which features employing certain chemical sensitizers in combination with a substance which reduces fog. Still another object of this invention is to provide novel sensitization of photographic elements having a light sensitive, vacuum deposited silver halide layer, with sensitizers in combination with certain substances which function to reduce fog. Other objects of the invention will appear herein.

In accordance with this invention, photographic elements having a light sensitive binder-free deposit of silver halide coated on a support are chemically sensitized with a chemical sensitizer in combination with a suitable compound which coacts with the chemical sensitizer to reduce fog.

In one embodiment of the invention, a photographic element having a binder-free deposit of silver halide is chemically sensitized with a gold salt, a silver salt, or a salt of a Group VIII metal having an atomic weight in excess of 100, in combination with a sulfur-containing ice compound which coacts with the chemical sensitizer to substantially reduce or eliminate fog.

In a preferred embodiment of the invention, photographic elements having a vacuum deposited layer of light sensitive silver halide are sensitized with a gold salt in combination with a thiosulfate and a thiocyanate salt, such as the alkali metal or ammonium salts thereof. It has been found that when vacuum deposited silver halide layers are sensitized in accordance with this procedure, a substantial increase in the sensitivity of the element is realized without the appearance of undesirably high fog.

In one method of sensitizing photographic elements having a binder-free deposit of silver halide in accordance with the invention, the photographic element is bathed in a solution containing a combination of chemical sensitizer and a substance which coacts with the chemical sensitizer to reduce fog. If desired, the photographic element may be first bathed in the fog-reducing compound, and then in a solution containing the chemical sensitizer. Alternatively, the photographic element may be bathed first in a solution containing a chemical sensitizer, and then in a solution containing fog reducer. In the latter case, it is highly desirable to bathe the element in the solution containing the fog reducing agent substantially immediately after bathing it in the solution containing the chemical sensitizer in order to etfectively control fog.

In another method of sensitizing photographic elements having a binder-free silver halide layer in accordance with the invention, the photographic element is provided with an arrangement wherein the light sensitive layer has a contiguous hydrophilic coating containing the combination of chemical sensitizer and iog-reducing agent. Preferably, in sensitizing in accordance with this method of the invention, a support is provided having thereon a binder-free light sensitive silver halide layer, and has coated thereover a hydrophilic substance containing the combination of chemical sensitizer and fog-reducing agent.

Our invention will be further illustrated in the following example.

EXAMPLE 1 A series of paper supports had vacuum deposited thereon silver bromide at a thickness of about 0.1 to 5.0 microns, and the silver bromide layer was then overcoated with a thin layer of hardened gelatin. One film strip was then bathed for 5 minutes at 68 F. in Solution 1 consisting of 4 mg. potassium chloroaurate in 200 cc. distilled water, the pAg being adjusted to 8.5 with dilute potassium bromide. Another film strip was bathed for 5 minutes at 68 F. in Solution 2 which consisted of 4 mg. potassium chloroaurate and 10 mg. sodium thiocyanate in 200 cc. distilled water. A third film strip was bathed for 5 minutes at 68 F. in Solution 3, which was the same as Solution 2 except that 2 mg. of sodium thiosulfate were added. The film strips were then exposed to room lights for 10 seconds through a step wedge and developed for 10 seconds in the following developer:

Grams Methyl p-aminophenol 3.1 Sodium sulfite, des. 45.0 Hydroquinone 12.0 Sodium carbonate 67.5 Potassium bromide 1.9 Sodium thiosulfate 2.5

' Water to make 1 liter.

The strips were all then stopped, fixed and washed in the usual manner. Comparison of the three strips which had been bathed in the solution containing gold salt showed approximately four times as great a speed :as that of the control, which had not been treated in any bath. The fog in each of the strips was determined and is shown in the following table:

Table 1 Treatment: Fog Control 0.04 Solution 1 heavily fogged Solution 2 0.32 Solution 3 0.07

It may be seen in Table 1 that the sensitizing combination of the invention drastically reduces fog. The combination of sodium thiosulfate and sodium thiocyanate demonstrates unexpected coaction in providing a very low fog level.

In accordance with the invention, a large variety of silver or gold salts or salts of metals of Group VIII which have an atomic weight over 100, may be employed as sensitizer. Exemplary of latter groups of salts are the water-soluble metal compounds represented by the following general formula:

wherein R represents a hydrogen atom, an :alkali metal atom or an ammonium radical, M represents a metal atom selected from Group VIII of the periodic arrangement of the elements having an atomic weight greater than 100, i.e., ruthenium, rhodium, palladium, osmium, iridium and platinum, and X represents a halogen atom, e.g., a chlorine or bromine atom. Still other metal compounds which we employ in practicing our invention are those which are represented by the following general formula:

R M'XC,

wherein R represents a hydrogen atom, an alkali metal atom or an ammonium radical, M represents a palladium or a platinum atom, and X represents a halogen atom. Examples of such metal compounds are ammonium and potassium chloropalladate, ammonium, sodium and potassium chloroplatinate, ammonium, potassium and sodium bromoplatinate, ammonium chlororhodate, ammonium chlororuthenate, ammonium chloroiridate; ammonium, potassium and sodium chloroplatinite, ammonium, potassium and sodium chloropalladite, etc.

A particularly useful class of sensitizers in accordance with the invention are the soluble gold compounds, such as the gold halides, e.g., auric chloride, or complex gold halides such as potassium auric chloride, sodium aun'c chloride, potassium or sodium auric bromide, potassium or sodium auric iodide, complex gold salts such as auric sulfate, alkali metal aurous thiosulfates, alkali metal aurous sulfites, complex salts formed by interaction of thiourea and auric chloride, and complex salts such as gold thiosinamine complexes, etc. An especially useful group of gold sensitizers are the salts which contain both gold and sulfur atoms, such as sodium aurous thiosulfate, potassium aurithiocyanate, 2 aurosulfobenzathiazole methochloride, and aurous sulfide, etc. Such salts show reduced tendency to cause background fog although it is desirable to have, in addition to such gold salts, a substance which coacts therewith to further reduce fogging.

The substance which we employ in combination with the chemical sensitizers preferably is a sulfur containing compound. Typical sulfur compounds which may be employed are sulfur compounds containing C=S or S-S-- groups, such as thiourea, allyl isothiocyanate, thiosinamine, etc. Also useful are metal and ammonium thiocyanates, e.g., potassium, sodium, ammonium, cadmium or calcuim thiocyanates; cystine, ,B-ethyl xanthate propionic acid, and the like.

If desired, the chemical sensitizer and fog reducing compound employed in this invention may be incorporated in a layer contiguous to the binder-free silver halide layer, such as a colloid layer composed of a hydrophilic substance such as gelatin, polyvinyl alcohol, a far hydrolyzed cellulose ester, such as water soluble cellulose acetate, and other hydrophilic substances such as those referred to in US. Patent 3,039,873, column 13.

The photographic elements of this invention may be spectrally sensitized in any convenient manner, such as by bathing in suitable solutions of a sensitizing dye such as the cyanine or merocyanine dyes.

The binder-free silver halide photographic elements of this invention are preferably prepared by vacuum deposition of a suitable silver halide or silver halides onto a support, for example, by the method described by De Boer et al., U.S. Patent 1,970,496 or Manfeld US. Patent 2,945,771. If desired, the evaporated silver halide layer may be provided with a contiguous, vacuum deposited alkali metal salt layer to increase the speed as described in Rasch and Hodges, U.S. patent application Ser. No. 361,243, filed Mar. 20, 1964.

This invention provides a highly convenient method of sensitizing light sensitive deposits of binder-free silver halide. In using the same sensitizers in conventional silver halide emulsions, it is necessary to digest the emulsions at elevated temperatures. No digestion is required in sensitizing the photographic elements of this invention.

In conventional emulsions, sulfur compounds, such as sodium thiosulfate and sodium thiocyanate, function as sensitizers and actually may cause fogging unless careful control is exercised. Thus, the present activity of such compounds as antifoggants was completely unexpected.

The invention has been described in detail with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the in- Vention as described hereinabove and as defined in the appended claims.

I claim:

1. A photographic element having a light-sensitive binder-free vacuum-deposited layer of silver halide coated on a support, said silver halide being chemically sensitized with a compound selected from the group consisting of silver salts, gold salts and salts of a Group VIII metal having an atomic weight in excess of 100, and containing an effective quantity of a thiosulfate salt and a thiocyanate salt to substantially reduce fog.

2. A photographic element comprising a support having vacuum deposited thereon a light-sensitive silver halide coating, said silver halide being chemically sensi tized with a gold salt and containing an effective quantity of a thiosulfate salt and a thiocyanate salt to substantially reduce fog.

3. A photographic element comprising a support having vacuum deposited thereon a light-sensitive silver halide coating, said silver halide being chemically sensitized with potassium chloroaurate and containing an effective quantity of sodium thiosulfate and sodium thiocyanate to substantially reduce fog.

4. A photographic element comprising a support hav ing a light-sensitive vacuum-deposited silver halide coating thereon, and having contiguous to said silver halide coating a hydrophilic colloid layer containing (1) a metallic salt selected from the group consisting of silver salts, gold salts and salts of a Group VIII metal having an atomic weight in excess of 100, said metallic salt being present in a concentration sufficient to chemically sensitize the silver halide, and (2) an effective quantity of a thiocyanate salt and a thiosulfate salt to reduce fog.

5. A photographic element comprising a support having a light-sensitive vacuum-deposited silver halide coating thereon, and having contiguous to said silver halide coating a hydrophilic colloid layer containing (1) a sufficient quantity of potassium chloroaurate to effectively sensitize the silver halide, and (2) an effective quantity of sodium thiocyanate and sodium thiosulfate to reduce fog.

6. The method of reducing fog in a chemically sensitized photographic element having a light-sensitive vacuum-deposited layer of silver halide coated on a support which comprises contacting the silver halide with a solution containing (1) a metallic salt selected from the group consisting of silver salts, gold salts and salts of a Group VIII metal having an atomic Weight in excess of 100, said metallic salt being present in a concentration sufiicient to chemically sensitize the silver halide, and (2) an effective quantity of a thiocyanate salt and a thiosulfate salt to reduce fog.

7. The method of reducing fog in a chemically sensitized photographic element having a light-sensitive vacuum-deposited layer of silver halide coated on a support which comprises contacting the silver halide with a solution containing (1) a sufficient quantity of potassium chloroaurate to effectively sensitize the silver halide, and (2) an effective quantity of sodium thiocyanate and sodium thiosulfate to reduce background fog.

References Cited UNITED STATES PATENTS 2,448,857 9/1948 Brice 96-110 2,597,915 5/1952 Yutzy et al 96--110 3,219,450 11/1965 Goldberg 96--94 OTHER REFERENCES Lu Valle et al.: AD Report 220,728, pp. l-4, 7-11 and 15 14, July 1959.

J. TRAVIS BROWN, Primary Examiner. 

